The annual 1-butene demand growth rate has been 3% to 4%, and 1-butene is being used as a monomer for copolymerization of high density polyethylene (HDPE) or linear low density polyethylene (LLDPE). Recently, the price of 1-butene has been increased due to a supply and demand imbalance caused by an increase in the price of naphtha and a decrease in the utilization rate of naphtha cracking process due to high oil price.
A C4 residue generally obtained from the naphtha cracking process is composed of butadiene, isobutene, 1-butene, 2-butene, normal butane, and isobutane, and a fraction, in which butadiene is separated from the C4 residue, is referred to as “C4 residue I” (mixture of isobutene, 1-butene, 2-butene, butane, and isobutane). A fraction separated after isobutene is reacted with methanol to prepare methyl tertiary butyl ether (MTBE) is referred to as “C4 residue II” (mixture of 1-butene, 2-butene, butane, and isobutane). Also, a fraction, in which a trace of butadiene is removed by introducing the C4 residue II into a selective hydrogenation reactor, is referred to as “C4 residue 2.5”.
In general, the production of 1-butene is performed in such a manner that a fraction remaining after separating isobutene from the C4 residue 2.5 is introduced into a distillation column to obtain 1-butene having a purity of 99% or more from the top of the column, and a C4 residue III, as a mixture of 1-butene, 2-butene, and normal butane, is obtained from the bottom of the column. The C4 residue III, with an overhead fraction of the isobutane distillation column, is prepared into liquefied petroleum gas (LPG) by a hydrogenation reaction. Also, the C4 residue III is separated into olefin and paraffin, and the olefin is concentrated to a concentration of 98 wt % of more and is then used to prepare methyl ethyl ketone (MEK) or prepare 1,3-butadiene by oxidative dehydrogenation. Furthermore, 1-butene and 2-butene are used to generate propylene through an exchange reaction or may be used to generate ethylene and hexane through an exchange reaction. In this case, in order to economically utilize the C4 residue II and the C4 residue III, 1-butene and 2-butene must be recovered from the resides (C4 residue II and C4 residue III) as much as possible, but since boiling points of the 1-butene and the 2-butene contained in the residues are very similar, it may not be possible to separate the 1-butene and the 2-butene by distillation unless using a lot of means. Thus, a significant amount of research related to a separation process of isobutene and 1-butene has been conducted, and a method of using isomerization of 1-butene and 2-butene has been introduced as a typical example.
Hereinafter, a conventional processing method will be described with reference to FIG. 1, wherein, as illustrated in FIG. 1, a conventional separation process has been performed by a process system including an isomerization reactor R1, a distillation column S1, a condenser C1, a reflux drum D1, a pump P1, and a reboiler B1. For example, an olefin fraction including isobutene, 1-butene, and 2-butene is supplied to the isomerization reactor R1 through a reactant supply line F1 and is then supplied to the distillation column S1 through a reaction product fraction transfer line L1 after a portion of the 1-butene is converted into 2-butene. The supplied reaction product is separated in the distillation column S1 so that a top fraction including isobutene is transferred to the condenser C1 through an overhead discharge line L2, condensed, and then introduced into the reflux drum D1 through reflux line 4 L3. A liquid in the top fraction in the reflux drum D1 is reintroduced into the distillation column S1 through reflux line 5 L4, and a gas is discharged through a recovery line L5. A bottom fraction including normal butene is transferred to a recovery line L8 through a bottom discharge line L6 and discharged, or is transferred to the reboiler B1, vaporized, and then reintroduced into the distillation column S1 through reflux line 6 L7. With respect to the conventional method as described above, since the isomerization reactor must not only be separately provided but also there is a need to use the condenser and reboiler, a process may be somewhat cumbersome and economic efficiency may not be good.
Thus, there is a need to develop a process which may easily recover normal butene from a reaction mixture including isobutene, isobutane, 1-butene, and 2-butene and may increase the economic efficiency while having high separation and recovery efficiency.